The control of the flow of informational molecules (mRNAs) from the nucleus to the cytoplasm is an important area of cellular and molecular biology about which very little is known. Recent evidence suggests the existence of a highly organized system in the nucleus which regulates the processing and transport of precursors to mRNA. A great deal of information about this system can be learned from studying the structure of the nuclear particles in which mRNA precursors are packaged, hnRNP. Unfortunately, it is not possible to purify and isolate hnRNP containing specific hnRNAs in order to study their structure. We propose to develop a system with which hnRNP containing specific transcripts of the investigator's choice can be isolated in sufficient quantity and purity to study their structure. This will be accomplished by inserting genes of interest into a non-defective adenovirus 5 expression vector under the control of an efficient promoter. Using this system, we will determine the polypeptide and snRNP composition of hnRNPs containing human histone H3, chicken Alpha-actin and mouse Alpha-globin transcripts (with and without their natural intervening sequences). We will also initiate studies on Alpha-globin and histone hnRNP with the ultimate goal of determining the fine structure of the pacticles.